Power over Ethernet
Gartner recommends that PoE technology be used to supply electricity to WLAN access points in all but the smallest installations.
There is a technological standard for PoE: the IEEE's 802.3af. However, it allows for two configurations and two methods of power injection. This may create compatibility problems for organisations using equipment from more than one vendor.
PoE is also needed for IP telephony over wired LANs. Organisations can significantly reduce the number of PoE ports needed at LAN edge switches by using wireless handsets rather than fixed ones.
Site planning
Building a WLAN that supports high-quality transmission of voice traffic is over twice as expensive as creating one for basic data services. In contrast to WLAN coverage for data applications, which can be limited to specific parts of an office complex, coverage for voice calls must be wider. It has to include every area of the workplace where calls can be taken. And, to support both data and voice traffic, a denser configuration of access points is required. This means a bigger, costlier network.
Where practicable, organisations should consider dedicating a WLAN channel to voice services. They should also buy equipment that lets users "roam" between access points without dropping calls.
Choice of technology
Most WLANs based on IEEE 802.11b -- today's most common standard -- support only eight to 12 simultaneous voice calls. Also, 802.11b, like 802.11g, supports only three radio channels. As a result, much rests on efficient re-use of those channels. Clearly, equipment based on these standards isn't ideal for use in large, busy offices.
From 2005, 802.11a equipment will be the best choice for these locations, which need a dense network of access points. The larger number of channels supported by 802.11a will make site planning much easier and let network managers assign sets of channels to specific services, such as voice calls.
Predicted use of voice-over-WLAN systems
Wireless PBX systems aren't new to corporate users. Systems that comply with the Digital European Cordless Telephone (DECT) specification, for example, have been available for over 10 years, but have never accounted for more than 12 percent of the PBX lines in service. This is because the benefits of wireless PBX systems have outweighed the additional costs only in certain industry applications and some small offices.
We don't expect transmission of voice traffic over WLANs to be popular in most large offices until two conditions are fulfilled:
VoIP client devices will account for about a third of large-office voice connections in 2008, by which time vendors will have lowered the price of WLAN systems and reduced the complexity required to support voice traffic. In view of this, we don't expect mainstream deployment of voice-over-WLAN systems in large offices before 2009. Before then, however, this technology will be deployed more and more by organisations in sectors such as warehousing and healthcare, where the business benefits clearly outweigh the costs. These systems will also crop up in more small offices, where frequent changes of location make a "portable" network highly attractive
